Undesired Emergency (UDE)

An undesired emergency, or UDE, is an application of a train's emergency brakes that was not initiated by the train crew. Instead of the engineer deliberately placing the brakes in emergency, the emergency application happens on its own, bringing the train to an abrupt, unplanned stop.

Common Causes

Most undesired emergencies come from a loss of air in the brake pipe that runs the length of the train. A common cause is an airhose separation - the air hoses between two cars coming apart - which dumps the air and triggers an emergency application throughout the train. Other causes include a broken trainline, a stuck or defective valve, or debris fouling a brake component. Because the air-brake system is designed to apply the brakes whenever brake-pipe air is lost, any such failure produces an emergency stop by design, which is the safe response to a possible break-in-two.

Response

When a UDE occurs, the crew must determine why the brakes went into emergency before proceeding. They inspect the train to find the cause - looking for a parted air hose, a separation between cars, or another fault - and correct it before recharging the brake system and continuing. Treating every undesired emergency as a possible separation or serious defect is an important safety practice, since the same event that causes a nuisance stop could also indicate that the train has come apart.